CD40L AND CD28 BLOCKADE INDUCES REGULATORY MECHANISM AND INHIBITS CHRONIC ALLOGRAFT REJECTION

Abstract

P1037 Aims: Blockade of individual T cell costimulatory pathways may result in long-term allograft survival but tolerance is not obtained since chronic rejection is observed. To obtain transplantation tolerance, blockade of more than one costimulatory pathway is needed but the importance of different pathways and the optimal reagents to be used have not been fully defined. Methods: Heart transplantation was performed between MHC mismatched rats. CD40-CD154 interactions were blocked by gene transfer of CD40Ig. We interfered with CD28 costimulatory signals by administering an anti-CD28 Mab, which in contrast to CTLA4Ig, preserves T cell inhibitory signals through CTLA4. Results: CD40Ig treatment resulted in long-term (>120d, n=19) heart allograft survival and development of chronic rejection in all grafts whereas acute rejection occurred in the non-coding adenovirus-treated (7.6±1.6d, n=9) group. Treatment with anti-CD28 Mab resulted in a moderate but significant prolongation of allograft survival (17.4±1.7d, n=10). Cotreatment with both CD40Ig and anti-CD28Mab resulted in long term allograft survival (>120d, n=7) and a significant reduction in the percentage and degree of vessels with chronic rejection lesions, with 3/7 grafts completely free of lesions and therefore tolerant. Splenocytes from cotreated tolerant recipients, but not those with chronic rejection (CD40Ig or cotreated), showed completely suppressed MLR responses against 1st but not 3rd party donor cells. T cells purified from splenocytes of tolerant cotreated recipients showed normal MLR responses indicating that among total splenocytes, non T cells inhibited the proliferation of T cells. Splenocytes from tolerant recipients but not those with chronic rejection lesions inhibited naïve MLR, indicating the presence of active tolerogenic mechanisms. Transfer of splenocytes from CD40Ig-treated recipients to naïve sublethaly irradiated rats conferred long term allograft survival (>120d, n=4 vs. 17 d, n=2 in controls). In contrast, transfer of splenocytes from CD40Ig+anti-CD28 cotreated rats, either tolerant or with chronic rejection lesions, did not prolong allograft survival (17d, n=3). Conclusions: The association of CD40Ig with anti-CD28 Mab resulted in decreased chronic rejection lesions and tolerogenic mechanisms different to those seen with CD40Ig.